Impact of Tobacco Smoke on Pediatric Kidney Function: Evidence from Urine Cotinine Levels

Background: Tobacco smoking is a well-established risk factor for the development of chronic kidney disease (CKD) in adults. Additionally, exposure to tobacco smoke impacts pediatric kidney function and the progression of CKD. Urine cotinine (uCot), a metabolite of nicotine, serves as a biomarker for tobacco smoke exposure and is a more reliable indicator of CKD risk compared to self-reported smoking. This study evaluated the association between uCot levels and pediatric kidney function. Methods: Data were extracted from the Korea National Health and Nutrition Examination Survey (KNHANES) conducted between 2019 and 2021. A total of 195 children aged 10–18 years were included in the analysis. The estimated glomerular filtration rate (eGFR) was calculated using the bedside Schwartz equation. Demographic and clinical characteristics of the study population were reported as weighted values. Weighted regression analysis was used to analyze the association between uCot levels and kidney function. Results: Of the 195 children, 68.2% were male, with a mean age of 15.3±0.2 years. The mean eGFR was 99.4±1.8 ml/min/1.73m2, and the mean urine albumin-to-creatinine ratio (uACR) was 7.1±0.5 mg/g. The mean uCot level was 327.0±50.5 ng/mL, and the mean uCot-to-creatinine ratio (uCCR) was 173.2±27.1 ng/mg. Among the children, 28.6% were exposed to secondhand smoke from parents, and 37.6% were smokers. Smoking was positively associated with uCot levels (p<0.0001) and uCCR (p<0.0001). However, parental secondhand smoke exposure did not show a significant association with uCot levels or uCCR. Both uCot levels (R2=0.07, regression coefficient estimate=-0.009, p<0.0001) and uCCR (R2=0.04, regression coefficient estimate=-0.01, p=0.0123) were negatively associated with eGFR. While smoking showed a significant negative association with eGFR (R2=0.02, regression coefficient estimate=-9.5, p<0.001), parental secondhand smoke exposure did not exhibit a clinically significant association with eGFR. Neither uCot nor uCCR showed significant associations with uACR. Conclusion: In conclusion, tobacco smoking negatively impacts kidney function in the pediatric population and can be monitored using uCot levels or uCCR. In this study, parental secondhand smoke exposure did not affect the kidney function of healthy children. Therefore, uCot levels in children could help identify those at high risk for developing CKD.